Method of treating stored wood chips



Sept. 10, 1968 l. LISS'ALBIN CROON ETAL 3, 0 ,085

METHOD OF TREATING STORED WOOD CHIPS Filed July 14, 1965 4 Sheets-Sheet 1 Fig.2

Sept. 10, 1968 LlSS-ALBIN CROON ETAL 3,

METHOD OF TREATING STORED WOOD CHIPS Filed July 14, 1965 4 Sheets-Sheet 2 Fig.3

Sept. 10, 1968 LISS-ALBIN CROON ETAL 3,

METHOD OF TREATING STORED WOOD CHIPS 4 Sheets-Sheet 5 Filed July 14, 1965 Fig.6 A

Sept. 10, 1968 I. LISSALBIN CROON ETAL 3, ,03

METHOD OF TREATING STORED WOOD CHIPS Filed July 14, 1965 4 Sheets-Sheet 4 0 1'0 2'0 3'0 4'0 5'0 0'0 days Temperature process where no heat was supplied C I Temperature process where heat was supplied Atmospheric temperature United States Patent 3,401,085 METHOD OF TREATING STORED WOOD CHIPS Ingemar Liss-Albin Croon, Alfretlshem, and Lars Gunuar Kjellander, Ornskoldsvik, Sweden, assignors to Domsjo, Mo och, Aktiebolag, Grnsiroldsvik, Sweden, a corporation of Sweden Filed July 14, 1965, Ser. No. 471,985 Claims priority, application Sweden, July 16, 1964, 8,717/ 64 8 Claims. (Cl. 195-8) ABSTRACT OF THE DISCLOSURE A method is provided for treating resiniferous wood chips which are stored in a pile for pulping, in order to enhance the enzymatic hydrolysis of resins in the wood chips so that the resins will be more readily extracted in the pulping. In the method, a sufficient portion of the chip pile is heated to a temperature of from about 1 to about 30 C. in order to initiate the enzymatic hydrolysis of resins in the wood chips and a substantially uniform temperature rise in the entire chip pile is permitted to occur.

The present invention relates to a method of storing wood chips.

In cellulose pulp factories, the wood can be stored as chips in chip piles. Such storage is used for various reasons in different types of factories. Thus, e.g., a sulfate pulp factory may use chip storage as a rational and inexpensive method of handling its wood, while a sulfite pulp factory also can utilize chip storage to improve the quality of the wood raw material.

In a wood chip pile there will normally occur, after a certain period of storage, temperatures above that of the surrounding atmosphere due to chemical and biological process. Temperatures within the range of 30 to 60 C. are common and still higher values may occur. In the warm and moist environment within the pile, the desirable enzymatic hydrolysis of the extractive substances of the wood will take place much more rapidly than in normal storage of logs, and at the same time the extractive substances are oxidized by atmospheric oxygen. These processes render it possible, after a short period of storage in a chip pile, to modify the extractive substances of the wood so that they will be readily solubilized in the sulfite pulping process, whereby a pulp of advantageously low extract content is obtained. Achieving the same low extract content by means of normal log storage requires considerably longer periods of storage of the wood raw material. However, a condition for achieving the above described modification of the extractive substances (resin) in a short period is that the temperature rise in the chip pile starts rapidly. Also, it is important that the temperature increase is uniform throughout the chip pile, so that a uniform quality of the stored chips is obtained.

In accordance with the technique hitherto employed, the chips are transported to the chip pile by means of a pneumatic conveyor system. The built pile is allowed to remain until the temperature rise sets in, which time can vary depending on the method of building the pile, the chip grade, the atmospheric temperature and other factors. Thus, it was found, e.g., that when a chip pile is built in winter when the temperature is below 0 C., the chips may be cooled during transport to the pile to temperatures around or below 0 C. If there are great quantities of cooled chips in the built chip pile, the exothermic processes will occur so slowly that no temperature rise will set in until after several months, when the atmospheric temperature has again increased to well above 0 C. In a chip pile comprising such cold portions, the de- 3,401,085 Patented Sept. 10, 1968 ice sired quality improvement by reactions of the extractive substances occurs very slowly, and as a rule a chip pile which is very uneven in quality is obtained, because the portions which were cold result in a pulp of high extract content, while other warmer portions of the chip pile result in a pulp of low rosin content.

The present invention aims at solving the problem of obtaining a uniform raise in temperature in a chip pile even when the pile is built in periods of low atmospheric temperatures. It was unexpectedly found that if during the buildup of the pile or a suitable time thereafter a suitable amount of heat is supplied to the chip pile at one or more times, the natural storage process can be initiated and carried through in a very short time: independently of the climatic conditions, and chips of very uniform quality be obtained. The method of this invention comprises the step of causing a local temperature rise to occur in the lower portion of the chip pile, during the first half of the period of storage, so that within the treated zone the chips achieve a temperature of at least 1 C. and at most 30 C., whereby a uniform temperature rise is initiated in the chip pile and the above mentioned advantages are obtained.

The amount of heat to be supplied in any particular case depends on the temperature of the chips. It Was found that as long as the chip material in the Zone of local heating has a temperature of 0 C., or lower, no exothermic enzymatic hydrolysis can start, while if one imparts to the chips a temperature of 1 C. or higher, such hydrolysis is initiated, which surprisingly enough rapidly results in a uniform temperature rise in the entire chip pile. In practice, it was found unnecessary and uneconomical to carry the local heating of the chips to above 30 C., and in most cases a temperature rise to between 1 C. and 15 C. will be sulficient. Especially advantageous results, from the point of view of heat economy, are in most cases obtained from a temperature rise of between 1 C. and 50 C., and it may in certain cases be more advantageous to carry out several heatings to this lower temperature at suitable intervals rather than a single heating to a higher temperature, e.g., if the local heating is carried out while the chip pile is being built.

The local heating should suitably be carried out in the lower half of the chip pile, since the warm vapors resulting from the exothermic reaction ascend through the pile, thereby spreading the exothermic reaction to the upper portions of the pile. Of course, the heat is also dissipated from the zone of local heating to other zones of the pile by radiation and conduction, wherefore good results will also be obtained if the local heating is applied to other portions of the chip pile. If the atmospheric temperature is low and a particularly rapid initiation of the enzymatic hydrolysis is desired, it will be advantageous to supply heat at one or more times while building the pile.

The invention will be described in more detail below with reference to the accompanying drawings, wherein:

FIGURE 1 shows a suitable device for supplying heat in top plan view;

FIGURE 2 shows a cross-section along line II in FIGURE 1;

FIGURES 3 and 4 and FIGURES 5 and 6 illustrate two other embodiments of a heat supplying device, in views similar to FIGURES 1 and 2; and

FIGURE 7 is a graph illustrating the effect of the method of this invention.

The local supply of heat can be achieved in various ways, such as by means of hot air, steam or electrical heating elements or the like. Usually, heating by means of steam or hot air is to be preferred in view of the reduced danger of local overheating (hot spots) and because these heating media are usually readily available at the site where the pile is built. A suitable device for heating in this manner is shown in FIGURES 1 and 2 and comprises a circular coil 1 with a pipe cross 2. The heating medium enters through the inlet 3 and flows out through apertures 4, which in the cross are arranged for vertical blowing and in the circular coil for blowing at an angle of 45 to the horizontal, as illustrated in FIG- URE 2. It is possible to replace the cross by a plurality of arms for the vertical blowing, in which case the circular coil may be excluded, as shown in FIGURE .3. A device of this type can also be provided with vertical end pipes for horizontal blowing toward the center, which end pipes may be foldable or detachable, as illustrated in FIGURE 4. A simple embodiment of the heating device comprises only a pipe cross and is shown in FIGURES and 6. It is of course also possible to let the blowing through the apertures 4 take place horizontally, as shown in FIGURES 3, 4, 5 and 6.

The following example further illustrates the method of this invention.

EXAMPLE A chip pile was built during March at atmospheric temperatures below 0 C. The dimensions of the pile were approximately 30 x 50 x 12 meters and its volume was approximately 11,000 cubic meters of loose chips. The chips were pine chips of an average solids content of about 42%. The pile was built by blowing the chips from a pneumatic conveyor. The pile comprised cold portions in which no temperature rise occurred until after about 2 months. FIGURE 7 shows examples of the temperature process in the pile, (a) in one end of the pile where no heat was supplied (the upper graph) and (b) in the opposite end of the same chip pile (the middle graph), where heat was supplied locally to the pile by blowing in steam by means of the device shown in FIGURE 1, which was positioned when the outermost portion of the pile was being built. Steam of 100 C. was blown into the pile for 2 periods of 15 minutes each while that portion of the pile was built. The temperatures in the treated and untreated portions of the chip pile were measured continuously for about 2 months by thermocouples positioned 2 meters above the ground and inserted 2 meters into the pile at corresponding points thereof. As seen from FIGURE 7, the heat supply resulted in a rapid initiation of the temperature rise in the heated part of the chip pile, while the part where no heat was supplied was at 0 C. for about 40 days before the temperature started to increase slowly.

The lower graph in FIGURE 7 shows the atmospheric temperature at the site of the pile for comparison.

We claim:

1. A method of treating resiniferous wood chips which are at a temperature of 0 C. or below and which are stored in a pile for pulping, in order to enhance the enzymatic hydrolysis of resins in the wood chips so that the resins will be more readily extracted in the pulping, which comprises heating a suficient portion of the chip pile to a temperature within the range from about 1 to about 30 C. in order to initiate the enzymatic hydrolysis of resins in the wood chips and permitting the temperature to rise substantially uniformly throughout the chip pile.

2. A method as in claim 1 in which the wood chips are heated to a temperature within the range from about 1 to about 15 C.

3. A method as in claim 1 in which the wood chips are heated to a temperature within the range from about 1 to about 5 C.

4. A method as in claim 1 in which the wood chips are heated during the first half of the period of storage of the chips.

5. A method as in claim 1 in which the wood chips are heated by blowing hot air through at least one part of the pile of chips.

6. A method as in claim 1 in which the wood chips are heated by blowing steam through at least one part of the pile of chips.

7. A method as in claim 1 in which the lower portion of the chip pile is heated.

8. A method as in claim 1 in which the chips are heated during the building of the chip pile.

References Cited UNITED STATES PATENTS 2,617,202 11/1952 Reedy 8 XR ALVIN E. TANENHOLTZ, Primary Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, 0.0. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OFF'QCORRECTION Patent No. 3,401,085 September 10, 1968 Ingemar Liss-Albin Croon et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 38 "process" should read processes Column 2, line 38, "50 C." should read 5 C.

Signed and sealed this 17th day of February 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

